Actually in my experience WW gets much more attention and better WOM than SMH. On websites WW's made headlines for WEEKS after OW, in BOT discussion about SMH's OW was dwarfed by WW's SIXTH weekend (everyone was like "OMG WW has amazing hold against direct competition"), even MCU-friendly site like KJ WW was also received very positively. In real life I see WW is like SW:TFA or Hamilton or BatB, like it's a cultural event that you HAVE to see to participate in conversation with friends or colleagues. Tw and IG are also full of stories like "My mother who goes to movie theaters 3 times in her life are asking me to take her to WW", etc.
Whereas SMH is just like other MCU movies, the only thing fresh is that it has a young cast. After seeing SMH on opening day I told my friends "It's great fun. I recommend if you're MCU fan or have money + time for it", I want to see once more, but I'll wait for 1 month for Superday/ discount. For WW I bought tickets for my family a day after and have seen it in theaters 4-5 times with my friends.
Tl;dr: There're good movies like Ant-Man, Doctor Strange or SMH. There're cultural events like WW. And sure if this was the first time ever we see Spider-Man in theaters then it would probably made 400M too, but it isn't.
DM as always been hot sell overseas so it's always expected for most movies to lose OS to DM. OS gross this year (and WW too) DM will take 4th place behind F8, TLJ and BatB. I think SMH can get to 850M and be the 2nd highest grossing Spider-Man worldwide, which is more than enough.